Homogeneous liddicoatite from Madagascar: a possible reference material? First EMPA, SIMS and SREF data
Aurisicchio, Carlo; Demartin, Francesco; Ottolini, Luisa; Pezzotta, Federicο
European Journal of Mineralogy Volume 11 Number 2 (1999), p. 237 - 242
published: Apr 19, 1999
manuscript accepted: Nov 27, 1998
manuscript received: Jul 18, 1998
ArtNo. ESP147051102013, Price: 29.00 €
Abstract The research of reference materials is of primary importance for the correct data processing with microbeam methods. In the case of silicates containing light and volatile elements, i.e., H, Li, Be, B and F, the problems of finding reference samples are enhanced by analytical difficulties and inhomogeneities in the chemical composition of natural phases. In this study, a large, pink-red coloured fragment of a tourmaline crystal from the Lacamisinten gem deposit (Fianarantsoa district, Central Madagascar) was investigated by different analytical techniques, e.g., electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS), crystal-Structure REFinement (SREF), atomic absorption (AA), thermogravimetric analysis (TGA) and gas-chromatography (GC) in order to assess its composition, structure and homogeneity. The EMPA study, carried out on three thin sections and a number of fragments, indicates an homogeneous composition in the liddicoatite-elbaite solid solution, with a high Mn content. The SIMS analyses on Li and H give results comparable with those from AA, and GC/TGA, respectively. B data, obtained by the ion microprobe, agree within 1.2-% rel. with those calculated by stoichiometry. The SREF data are in agreement with chemical analysis and show that this sample is homogeneous also by a structural point of view. Depending on these results it is probable that this sample (or a part of it) could be a good reference material for tourmalines of the liddicoatite-(Mn bearing) elbaite solid solution. Further studies, also in terms of 11B/10B isotopic ratios, are in progress to investigate more extensively any local variation in the chemical composition of the sample, and in order to identify the most homogeneous portion of the crystal that could be used as a reliable reference material for elemental as well as isotopic micro-analytical work.